Still Overheating
Thread Starter
Racer
Joined: Sep 2008
Posts: 403
Likes: 7
From: Space Coast Florida
Still Overheating
My 74' overheated after about 10 mins but it was sitting for awhile so I thought it was normal. So I changed the thermostat. Nothing. Changed the water pump. Nothing. I check coolant level daily and there seems to be no leaks. What else can be left? I turned on the AC and the temp rose about 100 degrees in less then 2 mins so I'm assuming somethings wrong still.. Could the thermometer be broken or is there something else that can be replaced? Thanks.
Drifting
Joined: Jun 2005
Posts: 1,523
Likes: 1
From: grand prairie texas
Assuming you werent expirencing any overheating problems before I would check lower radiator hose for collapsing. There is a spring inside the hose that could be rusted away. Check fan clutch. Possibly still air in the system. Posibly radiator finally got restricted flow .
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
when the car is hot touch the upper radiator hose. if there is a blockage somewhere it wont be as hot as it should be because the water wont be circulating.
you should be able to see the lower hose close up if the spring is bad.
you should be able to see the lower hose close up if the spring is bad.
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Are you sure you're overheating? Confirm the gauge is accurate by using an IR gun.
Also, overheating at idle is usually an indication that your clutch fan is faulty.
You may also have a radiator problem.
Also, overheating at idle is usually an indication that your clutch fan is faulty.
You may also have a radiator problem.
Pro
Joined: Mar 2005
Posts: 683
Likes: 4
Check the upper and lower radiator hoses. These hoses will become weak or if the spring inside has collasped the hose will also collaspse. This will reduce or even stop the flow of coolant. Did you do anything to the system before it started to overheat?
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Thread Starter
Racer
Joined: Sep 2008
Posts: 403
Likes: 7
From: Space Coast Florida
The car has sat for 18 years but never over heated before. Haven't had a chance to check if the hoses collapse yet, but was rust in the coolant when I drained the coolant so theres a good chance the spring has rusted out.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
.
I know its almost impossible to touch the radiator but you might check for cool spots....Meaning the radiators efficiency had deteriorated and may be plugged. If its warm all over its probably OK
I know its almost impossible to touch the radiator but you might check for cool spots....Meaning the radiators efficiency had deteriorated and may be plugged. If its warm all over its probably OK
Racer
Joined: Sep 2007
Posts: 288
Likes: 1
I had this same problem with my 68. Couldn't idle no time at all and it would overheat. Looking at the cooling fan while idleing it was turning. Long story short I went to junk yard and got different cooling fan and spacer to take up lost space when I removed the clutch. I put fender covers on before changing out clutch and fan. When I started the car the fender covers blew Off. No more heating problens..
charlie
Le Mans Master
Joined: Jan 2006
Posts: 6,506
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From: Butler Pa
I had this same problem with my 68. Couldn't idle no time at all and it would overheat. Looking at the cooling fan while idleing it was turning. Long story short I went to junk yard and got different cooling fan and spacer to take up lost space when I removed the clutch. I put fender covers on before changing out clutch and fan. When I started the car the fender covers blew Off. No more heating problens..
charlie
charlie
Burning Brakes
Joined: Dec 2008
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From: PURCELLVILLE VA
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Hi, I'm new to this site. I do have a suggestion. When I change thermostats I drill a 1/16 or 1/8 hole in the thermostat. It keeps that air bubble from forming under the thermostat which in turn will not allow it to reach the temp for it to open. Its a cheap simple fix, might work for you.
Drifting
Joined: Dec 2007
Posts: 1,634
Likes: 1
From: aurora
Assuming you werent expirencing any overheating problems before I would check lower radiator hose for collapsing. There is a spring inside the hose that could be rusted away. Check fan clutch. Possibly still air in the system. Posibly radiator finally got restricted flow .
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
YOu might have an air pocket somewhere in the motor preventing proper circulation. I always fill my motor thru the thermostat housing 
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
Long ago, I used to have the same kind of problems with my vette.
After changing many parts, including water pump, thermostat, fan clutch, temp sender,... and reverse flushing the engine block / cylinder heads and radiator core, check timing, richness and so on, I still had the same problems ( overheating in Summer when idling ) even if it was slightly better after all this work...
I finally decided to buy a new radiator ( copper core, OEM replacement, even if I regret today not to have bought an aluminum unit ! ).
Since this day ( it was 10 years ago ! ) : No problem any more, and the water temperature is now always between 180° and 200°F, never more, even in the most extreme climatic conditions ( up to 100°F outside ).
It was worth the money
After changing many parts, including water pump, thermostat, fan clutch, temp sender,... and reverse flushing the engine block / cylinder heads and radiator core, check timing, richness and so on, I still had the same problems ( overheating in Summer when idling ) even if it was slightly better after all this work...
I finally decided to buy a new radiator ( copper core, OEM replacement, even if I regret today not to have bought an aluminum unit ! ).
Since this day ( it was 10 years ago ! ) : No problem any more, and the water temperature is now always between 180° and 200°F, never more, even in the most extreme climatic conditions ( up to 100°F outside ).
It was worth the money
Last edited by 73StreetRace; Dec 9, 2008 at 03:37 AM.
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
Several reasons.
1. The clutch disengages the fan when it's not needed which relates to less noise and less wasted energy.
2. Clutchless fans are usually 4 blade where the clutch fans are 6 or 7 blade so there is more airflow when it's really needed.
3. I have witnessed 2 clutchless fans explode. Both times the radiator was destroyed and one time a blade came through the hood. Clutch fans inherently limit the rpm of the fan to a reasonable level.
4. I have a clutch fan on my 502 and it never goes above 180* even with a '69 small block radiator.
5. GM would not have spent the money and time to use clutch fans if they weren't an improvement over the clutchless fans.
1. The clutch disengages the fan when it's not needed which relates to less noise and less wasted energy.
2. Clutchless fans are usually 4 blade where the clutch fans are 6 or 7 blade so there is more airflow when it's really needed.
3. I have witnessed 2 clutchless fans explode. Both times the radiator was destroyed and one time a blade came through the hood. Clutch fans inherently limit the rpm of the fan to a reasonable level.
4. I have a clutch fan on my 502 and it never goes above 180* even with a '69 small block radiator.
5. GM would not have spent the money and time to use clutch fans if they weren't an improvement over the clutchless fans.
Racer
Joined: Sep 2007
Posts: 288
Likes: 1
Several reasons.
1. The clutch disengages the fan when it's not needed which relates to less noise and less wasted energy.
2. Clutchless fans are usually 4 blade where the clutch fans are 6 or 7 blade so there is more airflow when it's really needed.
3. I have witnessed 2 clutchless fans explode. Both times the radiator was destroyed and one time a blade came through the hood. Clutch fans inherently limit the rpm of the fan to a reasonable level.
4. I have a clutch fan on my 502 and it never goes above 180* even with a '69 small block radiator.
5. GM would not have spent the money and time to use clutch fans if they weren't an improvement over the clutchless fans.
1. The clutch disengages the fan when it's not needed which relates to less noise and less wasted energy.
2. Clutchless fans are usually 4 blade where the clutch fans are 6 or 7 blade so there is more airflow when it's really needed.
3. I have witnessed 2 clutchless fans explode. Both times the radiator was destroyed and one time a blade came through the hood. Clutch fans inherently limit the rpm of the fan to a reasonable level.
4. I have a clutch fan on my 502 and it never goes above 180* even with a '69 small block radiator.
5. GM would not have spent the money and time to use clutch fans if they weren't an improvement over the clutchless fans.
charlie
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Sounds like yours sorely needs a thorough chemical cleaning & flush of entire cooling system. Don't simply flush it, CLEAN it too. That rust collects in flues, jackets & passages; can/will cause eratic cooling. I dunno if still available at local GM dealer parts dept ... was under $10 ... heavy duty cleaner GM p/n 12346500 ... it works! Flush then clean then flush again then replace t'stat & cap.
Many posts here on cleaning cooling system; do a search if the above ain't sufficient.